1. Field of the Invention
The present invention relates to a mobile communications system and, more particularly, to a call setup system and method in a mobile communications environment.
2. Discussion of the Related Art
In the world of cellular telecommunications, those skilled in the art often use the terms 1G, 2G, and 3G. The terms refer to the generation of the cellular technology used. 1G refers to the first generation, 2G to the second generation, and 3G to the third generation.
1G is used to refer to the analog phone system, known as an AMPS (Advanced Mobile Phone Service) phone systems. 2G is commonly used to refer to the digital cellular systems that are prevalent throughout the world, and include CDMAOne, Global System for Mobile communications (GSM), and Time Division Multiple Access (TDMA). 2G systems can support a greater number of users in a dense area than can 1G systems.
3G is commonly used to refer to the digital cellular systems currently being developed. Recently, third-generation (3G) CDMA communication systems have been proposed including proposals, such as cdma2000 and W-CDMA. These 3G communication systems are conceptually similar to each other with some significant differences.
A cdma2000 system is a third-generation (3G) wideband, spread spectrum radio interface system which uses the enhanced service potential of CDMA technology to facilitate data capabilities such as Internet and intranet access, multimedia applications, high-speed business transactions, and telemetry. The focus of cdma2000, as is that of other third-generation systems, is on network economy and radio transmission design to overcome the limitations of a finite amount of radio spectrum availability.
FIG. 1 illustrates a wireless communication network 1 architecture.
Referring to FIG. 1, a subscriber uses a mobile terminal 2 to access network services. The mobile terminal may be a portable communications unit, such as a hand-held cellular phone, a communication unit installed in a vehicle, or even a fixed-location communications unit.
The electromagnetic waves from the mobile terminal are transmitted by the Base Transceiver System (BTS) 3 also known as node B. The BTS 3 consists of radio devices such as antennas and equipment for transmitting radio waves. The Base Station Controller (BSC) 4 receives the transmissions from one or more BTS's. The BSC 4 provides control and management of the radio transmissions from each BTS 3 by exchanging messages with the BTS 3 and the Mobile Switching Center (MSC) 5 or Internal IP Network 17. The BTS's and BSC are part of the Base Station (BS) 6.
The BS 6 exchanges messages with and transmits data to a Circuit Switched Core Network (CSCN) 7 and Packet Switched Core Network (PSCN) 8. The CSCN 7 provides traditional voice communications and the PSCN 8 provides Internet applications and multimedia services.
The Mobile Switching Center (MSC) 5 portion of the CSCN 7 provides switching for traditional voice communications to and from an mobile terminal and may store information to support these capabilities. The MSC 5 may be connected to one of more BS's as well as other public networks, for example a Public Switched Telephone Network (PSTN) or Integrated Services Digital Network (ISDN). A Visitor Location Register (VLR) 9 is used to retrieve information for handling voice communications to or from a visiting subscriber. The VLR 9 may be within the MSC and may serve more than one MSC 5.
A user identity is assigned to the Home Location Register (HLR) 10 of the CSCN 7 for record purposes such as subscriber information, for example Electronic Serial Number (ESN), Mobile Directory Number (MDR), Profile Information, Current Location, and Authentication Period. The Authentication Center (AC) 11 manages authentication information related to the mobile terminal. The AC 11 may be within the HLR 10 and may serve more than one HLR 10. The interface between the SC and the HLR/AC is an IS-41 standard interface.
The Packet Data Serving Node (PDSN) 12 portion of the PSCN 8 provides routing for packet data traffic to and from mobile terminal. The PDSN 12 establishes, maintains, and terminates link layer sessions to the mobile terminal's and may interface with one of more BS and one of more PSCN.
The Authentication, Authorization and Accounting (AAA) Server 13 provides Internet Protocol authentication, authorization and accounting functions related to packet data traffic. The Home Agent (HA) 14 provides authentication of MS IP registrations, redirects packet data to an from the Foreign Agent (FA) 15 component of the PDSN 12, and receives provisioning information for users from the AAA. The HA 14 may also establish, maintain, and terminate secure communications to the PDSN and assign a dynamic IP address. The PDSN 12 communicates with the AAA 13, HA 14 and the Internet 16 via an Internal IP Network 17.
FIG. 2 illustrates a data link protocol architecture layer for a wireless network.
Referring to FIG. 2, the upper layer contains three basis services; voice services 62, data services 61 and signaling 70. Voice services 62 include PSTN access, mobile-to-mobile voice services, and Internet telephony. Data services 61 are services that deliver any form of data on behalf of a mobile end user and include packet data applications (e.g., IP service), circuit data applications (e.g., asynchronous fax and B-ISDN emulation services), and SMS. Signaling 70 controls all aspects of mobile operation.
The Link Layer 30, is subdivided into the Link Access Control (LAC) sublayer 32 and the Medium Access Control (MAC) sublayer 31. The link layer provides protocol support and control mechanisms for data transport services and performs the functions necessary to map the data transport needs of the upper levels 60 into specific capabilities and characteristics of the physical layer 20. The Link Layer 30 may be viewed as an interface between the upper layers and the Physical Layer 20.
The separation of MAC 31 and LAC 32 sublayers is motivated by the need to support a wide range of upper layer services, and the requirement to provide for high efficiency and low latency data services over a wide performance range (from 1.2 Kbps to greater than 2 Mbps). Other motivators are the need for supporting high QoS delivery of circuit and packet data services, such as limitations on acceptable delays and/or data BER (bit error rate), and the growing demand for advanced multimedia services each service having a different QoS requirements.
The LAC sublayer 32 is required to provide a reliable, in-sequence delivery transmission control function over a point-to-point radio transmission link 42. The LAC sublayer manages point-to point communication channels between upper layer entities and provides framework to support a wide range of different end-to-end reliable link layer protocols.
The MAC sublayer 31 facilitates complex multimedia, multi-services capabilities of 3G wireless systems with Quality of Service (QoS) management capabilities for each active service. The MAC sublayer 31 provides procedures for controlling the access of data services (packet and circuit) to the physical layer 20, including the contention control between multiple services from a single user, as well as between competing users in the wireless system. The MAC sublayer 31 also provides for reasonably reliable transmission over the radio link layer using a Radio Link Protocol (RLP) 33 for a best-effort level of reliability. Signaling Radio Burst Protocol (SRBP) 35 is an entity that provides connectionless protocol for signaling messages. Multiplexing and Quality of Service (QoS) Control 34 is responsible for enforcement of negotiated QoS levels by mediating conflicting requests from competing services and the appropriate prioritization of access requests.
The Physical Layer 20 is responsible for coding and modulation of data transmitted over the air. The Physical Layer 20 conditions digital data from the higher layers so that the data may be transmitted over a mobile radio channel reliably.
The Physical Layer 20 maps user data and signaling, which are delivered by the MAC sublayer 31 over multiple transport channels, into a physical channels and transmits the information over the radio interface. In the transmit direction, the functions performed by the Physical Layer 20 include channel coding, interleaving, scrambling, spreading and modulation. In the receive direction, the functions are reversed in order to recover the transmitted data at the receiver.
Generally, a mobile terminal communicates traffic data through a synchronous channel. The mobile terminal receives overhead and paging messages for an incoming call over control channels. The mobile terminal then sends a response appropriate for the received page to a corresponding communications network.
A base station transmits the overhead message or page on a common channel such as forward paging channel (F-PCH), forward broadcast control channel (F-BCCH), and forward common control channel (F-CCCH). The overhead message is transmitted on F-PCH or F-BCCH and the paging is transmitted on F-PCH or F-CCCH.
A mobile terminal, when turned on, monitors all slots to receive overhead messages. After having received an overhead message, the mobile terminal can receive a page according to two kinds of modes.
First mode is a non-slotted mode. In the non-slotted mode, the mobile terminal monitors all slots to receive a page. Second mode is slotted mode. In slotted mode, the mobile terminal is turned on at a determined slot to monitor the corresponding slot and to receive a page. The mobile terminal is then turned off in other slots to reduce power consumption.
Whether the mobile terminal operates in non-slotted or slotted mode depends on a station class mask (SCM) value set in the mobile terminal. Generally, a mobile terminal is turned on one slot in advance of the determined slot in preparation of a paging reception. This is because preparation for hardware to normally operate is needed to receive a paging.
When a mobile terminal operates in slotted mode, (i.e., when the mobile terminal receives a page in a specific slot to monitor a corresponding paging slot), the following two situations may arise. First, if the value of the paging slot cycle increases, time during which the mobile terminal is turned on is decreased. This reduces power consumption, however, time taken for the mobile terminal to receive a page is prolonged and call setup is delayed. Second, if the value of the paging slot cycle decreases, the time during which the mobile terminal is turned on is prolonged. This increases the power consumption of the mobile terminal. The time for the mobile terminal to receive the paging is reduced, however, because the time taken for setting up the call is shortened.
A base station sets values of minimum slot cycle index (MIN_SLOT_CYCLE_INDEX) and maximum slot cycle index (MAX_SLOT_CYCLE_INDEX). Accordingly, all mobile terminals in a service domain of a corresponding base station determine a paging slot cycle value using the values of minimum cycle index (MIN_SLOT_CYCLE_INDEX) and maximum slot cycle index (MAX_SLOT_CYCLE_INDEX).
In the slotted mode, the mobile terminal is turned on once each predetermined cycle. Such a cycle is called a paging slot cycle. And, a corresponding slot monitored by the mobile terminal during the corresponding paging slot cycle is called a paging slot (PGSLOT).
The paging slot cycle can be found by Equation 1.C=16×2i, −4≦i≦7  [Equation 1]
In Equation 1, ‘i’ is a selected slot cycle index (SLOT_CYCLE_INDEXs). The selected slot cycle index (SLOT_CYCLE_INDEXs) is found by Equation 2 using three kinds of parameters, for example, preferred slot cycle index (SLOT_CYCLE_INDEXp), maximum slot cycle index (MAX_SLOT_CYCLE_INDEXs), and minimum slot cycle index (MIN_SLOT_CYCLE_INDEXs).SLOT_CYCLE_INDEXs=MAX(MIN_SLOT_CYCLE_INDEXs, MIN(SLOT_CYCLE_INDEXp, MAX_SLOT_CYCLE_INDEXs))  [Equation 2]
The preferred slot cycle index (SLOT_CYCLE_INDEXp) is a value stored in the mobile terminal and has a preferred value of −4 to 7. The value of the preferred slot cycle index (SLOT_CYCLE_INDEXp) is transmitted to a base station through one or two fields (SLOT_CYCLE_INDEX, SIGN_SLOT_CYCLE_INDEX) in registration message (RGM), Origination message (ORM), page response message (PRM), or terminal information message.
The minimum slot cycle index (MIN_SLOT_CYCLE_INDEXs) has a preferred value of −4 to 0. The maximum slot cycle index (MAX_CYCLE_INDEXs) has a preferred value of 0 to 7. The value of the maximum slot cycle index (MAX_SLOT_CYCLE_INDEXs) is transmitted to the mobile terminal from the base terminal through system parameters message (SPM) or MC-RR parameters message (MCRRPM).
The paging slot (PGSLOT) is found by Hashing using a phone number of the mobile terminal. One corresponding value is selected from the group consisting of 0 to (C−1), where ‘C’ is the value of paging slot cycle calculated by Equation 1. FIG. 3 illustrates a case where the values of the preferred slot cycle index (SLOT_CYCLE_INDEXp), maximum slot cycle index (MAX_SLOT_CYCLE_INDEXs), minimum slot cycle index (MIN_SLOT_CYCLE_INDEXs), and paging slot (PGSLOT) are 2, −1, 3, and 6, respectively.
Based on Equation 2, the value of the selected slot cycle index (SLOT_CYCLE_INDEXs) is ‘2’. That is, the value of the selected slot cycle index (SLOT_CYCLE_INDEXs) is max[−1, min(2,3)] which is equal to ‘2’. Moreover, based on Equation 1, the paging slot cycle becomes 16×22, (i.e., ‘64’ by applying the value ‘2’ of the calculated slot cycle index (SLOT_CYCLE_INDEXs) to ‘i’).
Slot numbers are repeated from 0 to 2047. Hence, as shown in FIG. 3, because the paging slot cycle is 64 and the paging slot (PGSLOT) is 6, the mobile terminal sequentially monitors the slot numbers 6, 70, 134, and 198.
In the above-explained related art, if the mobile terminal, which previously had a data call that was released, subsequently tries a call access the mobile terminal will have to wait for the duration of the entire cycle. It is necessary to set up separate parameter values to a specific mobile terminal to reduce a time delay for receiving a paging for the call access. This is because it is highly probable that the mobile terminal, which had setup the call that was released, will try to setup a call again.
Currently, all mobile terminals that communicate with the same base station use the same values of the maximum slot cycle index (MAX_SLOT_CYCLE_INDEXs) and minimum slot cycle index (MIN_SLOT_CYCLE_INDEXs). Hence, when a particular mobile terminal tries to setup a call connection with the base station, the time taken for receiving the page from the base station is delayed. Therefore, a fast call setup method and system is needed.
There is a higher probability that a mobile terminal, which recently had a call release, to setup a call again, compared with other mobile terminals attempting to setup a new call. In other words, there is a high probability that a page for connecting a call will be sent to the mobile terminal that has recently released the call.